Hopefully this won't be taken as frivolous.  I (and possibly some of you) have been convinced by the argument at http://tauday.com/.  It's very convincing, and I won't rehash it here.

The use of τ instead of π will only become really convenient when one does not have to preface everything with "let τ = 2π".

For example, in D, in order to think in terms of τ instead of π, one must define `enum real TAU = std.math.PI * 2;`, and possibly also TAU_2, TAU_4, etc.

As well as being a typing inconvenience, I also think things are not that easy due to loss of precision (though I'm far from an expert on intricacies of floating point).

There is an initiative to add TAU to the Python standard library: http://www.python.org/dev/peps/pep-0628/

To this end, I suggest adding the constant TAU to std.math, and possibly also TAU_2 as an alias for PI, TAU_4 as an alias for PI_2, TAU_8 as PI_4.

In any case, I'd like to know what's necessary in order for me to define these constants without loss of precision.
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